This post was published long before the Mists of Pandara Expansion.
The tips and techniques explained here may be outdated.

Macro: Healthstones

[Deprecated: with the 3.0.x patch, you can only carry one healthstone. So the macro is still useful.. just not as useful as it used to be.]
The following macro will allow you to have a single button for multiple healthstones. If you have all three sizes, then clicking this once will use the biggest one. Then the second click (after 2 mins) will use the middle sized one. Clicking this a 3rd time (after 2 mins) will use the smallest healthstone.

It will show as a tooltip the smallest healthstone. Assuming you have one in your inventory the icon will show up until you use the smallest healthstone.